Imidafenacin is a compound having an antagonistic action in respect of muscarinic receptors M3 and M1 (see Patent Document 1 specified below), and it is put at service as a medicament for treating overactive bladder (see Non-Patent Document 1 specified below). As pharmaceutical preparations comprising imidafenacin as a main active ingredient, there have been known, for instance, an orally-administered solid pharmaceutical preparation and a transdermal therapeutic system, each of which contains imidafenacin (see Patent Documents 2 and 3 specified below).
More specifically, Patent Document 2 discloses that the imidafenacin-containing pharmaceutical preparation is photosensitive and that the pharmaceutical preparation in the form of a tablet is correspondingly covered with a coating liquid which contains titanium oxide and iron sesquioxide to thus make the tablet photo-stable. However, Patent Document 2 relates to a product prepared by compressing an imidafenacin-containing granulated product into tablet and then applying a coating onto the resulting tablet and this Patent Document does not discloses any orally rapidly disintegrating tablet at all.
In addition, Patent Document 3 relates to a pharmaceutical preparation of the transdermal therapeutic system type and therefore, the pharmaceutical preparation disclosed therein is different from the orally rapidly disintegrating tablet in the dosage form.
Incidentally, Patent Documents 4 and 5 each disclose a method for the preparation of an orally-administered pharmaceutical preparation. However, Patent Documents 4 and 5 relate to a method for the preparation of a pharmaceutical preparation in a sustained release type dosage form. Accordingly, a gel-forming substance is used in the dosage form disclosed in Patent Document 4 and the tablet formed using such a gel-forming substance cannot be a disintegrating one. Moreover, in respect of the pharmaceutical preparation disclosed in Patent Document 5, this document does not disclose that starch, as an excipient, in an amount of not less than 40% by mass is used when granulating imidafenacin to thus considerably improve the photostability of the resulting pharmaceutical preparation.
On the other hand, there have intensively been conducted the development of pharmaceutical preparations while introducing improvements in manufacturing formulations into the development thereof, with the objective of improving the “Quality of Life (QOL)” of a patient. Most frequently or vigorously developed pharmaceutical preparations are orally rapidly disintegrating tablets, among others. The orally rapidly disintegrating tablet can instantaneously be disintegrated in the presence of even a small amount of saliva within the oral cavity and accordingly, the tablet can easily be administered to a patient and may be an optimum pharmaceutical preparation for administering it to elderly peoples and children who cannot swallow the tablets with ease. In addition, the tablet of this type may have such a merit that it can be taken without any help of water and accordingly, there is not any limit in the place and/or time for the administration thereof.
However, it would be quite difficult to apply a coating comprising titanium oxide and iron sesquioxide, to the orally rapidly disintegrating tablet while ensuring the maintenance of the disintegration property of the tablet and accordingly, there has not yet been proposed any report on the orally rapidly disintegrating tablet containing imidafenacin as an effective component.    Non-Patent Document 1: Bioorg. Med. Chem., 1999, Vol. 7, pp. 1151-1161;    Patent Document 1: JP-A-7-215943;    Patent Document 2: WO 01/34147 A1 pamphlet;    Patent Document 3: WO 2006/082888 A1 pamphlet;    Patent Document 4: WO 2005/011682 A1 pamphlet;    Patent Document 5: WO 2006/0808481 A1 pamphlet.